Whisk together dry ingredients in a small bowl and set aside. In a large bowl with a handheld electric mixer or a stand mixer, beat butter, sugars, egg and vanilla until fluffy, about 2-3 minutes. Add the dry ingredients and chocolate chips together. Mix until combined. Press into the prepared pan and bake for 18-20 minutes until light golden brown. Don't overbake! These bars are definitely better underbaked by just a few minutes rather than being overbaked so watch them carefully. Let cool completely on a wire rack before slicing into squares.